Adds Hardness to Bar?:
Takes a LONG time to cure/harden, but after a 5 or 6 week cure, yes, a nice hard bar.
Creates Fluffy Lather?:
Nope! Quite the opposite of fluffy lather. One soaper I know describes the lather that 100% olive oil soap makes as "like snot." It is a kind of thick, sticky, creamy (some might say slimy) lather - quite unlike any commercial soap made.
Creates Stable Lather?:
It's stable...but just not very profuse...
Adds Moisturizing Qualties?:
Yes! That's what olive oil is great for - it's great for your skin and makes a wonderful, stable, creamy, moisturizing bar of soap!
While I'm sure that Granny used mostly tallow or lard to make her notorious lye soap, most soap makers today rely on a healthy portion of olive oil for theirs. Many use it as their primary soap making oil.
Why? Primarily for its wonderful moisturizing qualities - and for the fact that it blends well with other oils. While "Castille soap" - pure olive oil soap has a sort of thick, low lather, when mixed with some coconut, palm and castor, olive oil makes truly outstanding soap.